Dr. Garry Lacefield

Grass Tetany

January 2012 Article

Early spring is the primary time that farmers experience problems and loss of livestock to the forage related disorder known as grass tetany, grass staggers, lactation tetany, or hypomagnesemia. Grass tetany is a metabolic disorder caused by reduced magnesium (Mg) levels in the animal’s blood. High levels of Nitrogen (N) and Potassium (K) in the soil can increase the risk of grass tetany. It generally effects older, lactating cows but is also seen in dry cows, young cows, and, in rare cases, growing calves. Young cool-season grasses and small grains are commonly associated with this disorder. Grass tetany is most frequent in the spring but may occur in the fall and winter when these forages start growing rapidly or when cereal grain forages are fed.

Symptoms may consist of nervousness, lack of coordination, muscular spasms, staggering, convulsions, coma, and death. If there is a suspicion of grass tetany, a veterinarian should be called immediately.

Feeding high magnesium or high “Mag” mineral supplements, containing magnesium oxide, is the preferred method to reduce the occurrence of grass tetany. High “Mag” mineral mixes are available at most feed stores. Producers can also mix their own by adding the appropriate amount of magnesium oxide to another supplement or feed where the intake is controlled, i.e. feeding in or with 1 to 2 lbs. of corn or other by-product. Livestock should be fed this supplement starting in December or January and continued until spring time when temperatures are consistently above 60°F. To provide adequate amounts, 20 g of magnesium must be provided and consumed daily. Free-choice minerals should contain 12 % to 15% magnesium (from magnesium oxide) and cattle need to consume 4 ounces of the mineral. It is important to monitor intake to be sure cattle are consuming adequate amounts each day to provide protection against grass tetany. Lactation doubles Mg need and early plants do not take up Mg fast enough to provide adequate amounts.

The season for grass tetany is around the corner. To reduce health problems and loss of livestock to this disease, it is important to provide a quality, “high Mag” mineral or magnesium oxide containing supplement. Ask your county agent, veterinarian, or nutritionist for more information on supplementing Mg during periods of high risk.

“Grass tetany is a metabolic disorder caused by reduced magnesium levels in the animal’s blood”